U.S. Pat. No. 4,402,272 to Lehl et al. discloses a transportation system which includes an aircraft guided along an elevated rail. The aircraft has wheels which roll on the rail structure when the vehicle is operating at low speeds such as when it is approaching or departing from terminal areas. The aircraft normally travels along the rail in airborne flight at high speed and is guided along the rail by a system that includes sensors and controls for adjusting the flight path according to inputs received from the sensors. In this manner, the aircraft and rail system accommodate slow speeds in terminal areas and high speeds between terminals.
Although this type of system has considerable potential to achieve efficiencies in the transportation of passengers and cargo, further development work has indicated that there is room for improvement. In particular, the need for an air bearing between the guide rails and the aircraft involves considerable complexity both in the structures of the aircraft and rails and also in the pneumatic system required to supply air for the air bearing. The guide rail disclosed in the '272 patent is complicated and thus expensive to construct, primarily because the air bearing requires two round rails spaced apart from one another. The guide rail structure has two vertical plates, a top plate, the two round rails, and ribs that connect the rails with the rest of the structure. This complicated construction involves considerable expense.
The guidance system of the aircraft is likewise rather complicated. Two concentric tubes are required to surround the round guide rails and provide the air bearing. In addition, a manifold and hose system is required to direct the air to the air bearing. The overall result is that the system is characterized by considerable complexity which increases the cost, the maintenance requirements, and the potential for operational and safety problems.